Such lock and key systems of the kind known from the above mentioned US patents (Bo Widén) provide a high level of security as compared to conventional systems without rotatable tumblers and pivoting fingers thereon. A great number of code combinations can be achieved, and the locks are very difficult to pick or manipulate. The tumblers are only partially visible in the key slot, and their correct elevational and pivotal code positions are hidden from inspection through the key slot. Therefore, the particular code positions cannot be determined from just observing the key slot or even by sensing the finger positions with a tool.
The side code portions of the wave-like guiding surface (sometimes also called side bitting) of the key blade of the previously known key are each constituted by a concavity surface portion having two upwardly sloping surface portions adjoining smoothly on each longitudinal side thereof. These concavity surface portions can be located at a number of predetermined vertical levels at the side of the key blade. More specifically, it follows that the highest vertical level for the side code portions will be located at a vertical level which is somewhat lower than the uppermost part of the side material region where the wave-like guiding surface is cut, so as to accommodate the vertical extension of the adjoining sloping portions. A typical prior art key of this kind is shown in FIG. 28.
The possible number of side code portions associated with a particular side locking tumbler for a code structure involve different combinations of predetermined vertical levels and a number of longitudinal positions in relation to the side locking tumbler. In a typical system, which has been in commercial use for many years, the number of side tumblers is five (in addition to six centrally located tumblers cooperating with an upper edge of the key blade). The side material region, where the wave-like guiding surface or side bitting is cut at the side of the key blade, has a relatively small height (perpendicularly to the longitudinal direction of the key blade), such as about 2,0 mm (about 0.080 inches). Therefore, only a limited number of vertical levels can be accommodated while clearly differentiating between different codes, in particular two such levels, 0.60 mm (0.024 inches) and 1.20 mm (0.048 inches), respectively, calculated from the bottom edge of the key blade.
Such differentiated levels pertain to a particular pivotal position of the finger of the associated side locking tumbler. In the embodiment used hitherto, there are two vertical levels corresponding to each pivotal end position of the finger (at a pivotal angle of +15° and −15°), and two further levels corresponding to an intermediate pivotal position (at a pivotal angle of 0°), each being slightly higher than the first-mentioned levels, viz. 0.90 mm (0.036 inches) and 1.50 mm (0.060 inches), respectively. The reason why the vertical levels of the code portions at the 0° pivotal angle are somewhat higher than those at the pivotal end position angles is that the difference or mutual distance between the adjacent pivotal positions is too small to give a clearly differentiated code. The difference becomes greater when the vertical level as well as the longitudinal position are different.
Accordingly, for each side locking tumbler in the example above, there are six possible codes, viz.                two code portions at different vertical levels corresponding to a pivotal end position at +15°        two code portions at different vertical levels corresponding to a pivotal end position at −15°, and        two portions at different, slightly higher vertical levels corresponding to an intermediate pivotal position,making a total of six possible code portions for each side locking tumbler or a total of 65=7776 different combinations.        
Of course, it would be desirable to even further increase this relatively high number of combinations. However, the dimensions of the keys are greatly standardized and also adapted to existing manufacturing facilities. So, the only possibilities seem to be to either pack the vertical levels closer together, which would mean too short a vertical difference of less than 0.50 mm (0.020 inches) between such packed levels, or to use more than three different pivotal positions, which is however also not possible because of the very small longitudinal differences that would follow from such a modification.